SouthGobi has been informed by the IAAC that the 32-year-old "is no longer a suspect in their investigations", the coal firm said in a statement to the Hong Kong stock exchange where it is listed.

"The IAAC has informed the company that she will shortly be able to leave the country," SouthGobi said.

The Australian was barred from boarding a flight from Ulan Bator to Hong Kong in October as Mongolian authorities probed a corruption case, triggering calls from Armstrong's mother to let her daughter return home.

Officials wanted to question Armstrong as a witness to alleged corruption and money-laundering, although details of the case have remained sketchy.

Mongolian officials said Armstrong was wanted over an investigation into the former chief of Mongolia's mining authority, who is suspected of illegally handling mining licences, according to Dow Jones Newswires.

SouthGobi said the IAAC was continuing its probe into "the divestment of certain SouthGobi licences to third parties" and the "involvement and conduct of government officials" linked to the case.